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The knowledge of the dash cam lens

The dash cam lens is to gather light on the image sensor, which is the equivalent of a convex lens. If it only uses one convex lens glass, it can get the image completely, but the quality of the picture is very poor, in other words, the quality of the lens will directly affect the image effect, what is the difference between the lens? Before we go into this question, we need to learn about the parameters and terminology associated with the lens.

Focal length: the focal length refers to the distance from the center of the lens to the focal point. The HD dash cam uses a lens with a small focal length that is generally about 2.8 mm.One of the features of this short focal lens is the ability to pull out images that are clearer in the distance and near.

Aperture: the aperture is the focal length or clear aperture diameter. The larger the clear aperture, the more light is received and the brighter the image is, so the clear aperture is an important parameter on the dash cam. Obviously, the smaller the value is the better. The usual clear aperture of dash cams are around 2.8, but they will be more expensive to sell.

Visual angle: the visual angle is also known as visual range, divided into horizontal perspective and vertical perspective. If without the specification, it refers to the horizontal perspective. The horizontal perspective refers to the angle between the leftmost and rightmost view of the picture. The larger the angle, the wider the range.

And the vertical perspective is the angle between the top and bottom of the screen and the lens. Since our example is either 4：3 or 16：9, the ratio of the horizontal to vertical is also fixed. The diagonal angle is the angle between the upper left and lower right corner of the lens.

It is obvious that the value is larger than the first two. Some businesses call a diagonal angle a perspective when they claim a range of views, which is a bit fraudulent. So in confirming the range of visual angle, you must ask clearly and then make a judgment.

Resolution: it is a parameter that reflects the ability of the lens. This parameter gives you an intuitive sense of whether the image is sharp or not. Use a simple diagram to illustrate:

Above are three rows of black and white vertical bars; a first line is a physical object, it is some black stripes printed on white paper, its edge is clear, the second and third lines are taken with the camera, its edge is a little less black and white. It’s a black to white gradient.

As you can see from the diagram, the second line is clearer than the third line, which means that the second line has a higher resolution. In other words, if the line in question is farther away, the third line will become a mold, and the second line will be able to tell that it is made up of some lines. In other words, the lens in the second line has a higher resolution than the third line.

So this is also a very important parameter, but it is not given, and the difference between the individual lens is relatively large.

Light Transmittance: it is the ratio of the intensity of light passing through to the intensity of the light shining on it. Obviously, the better the transmittance, the brighter the lens image. This is related to the lens technology and materials.

Distortion: Because the recorder needs a larger angle to record more events, a wide-angle lens is often used, which can easily deform the images taken. Things that are straight are often photographed in the shape of an arc.

This is distortion, which makes the image look uncomfortable, and fortunately, there is little requirement for this parameter on the recorder.
After saying some terms, I’ll talk about the process; how good lenses and differential lenses are produced.

First of all, we should talk about the optical scale. As mentioned earlier, even if it can be imaged with a convex lens, the quality of the image is poor. The actual lens will be made up of multi-layer glass, which can give a clear image. The design depends on the design requirements.

Lenses can be made up of glass or resin, a plastic. Class lenses are made from optical glass and resin lenses are molded, so when processing in large quantities, there is a good cost advantage to the fat lenses.

The optical properties of the resin lenses are good, but one fatal drawback is that the coefficient of thermal expansion is high, and when the temperature is high, it deforms. When the car is exposed to the sun and the temperature in the car can reach more than 70 degrees, the resin lens may not be enough.

So the car recorder had better choose the full glass lens; plastic lenses have the risk of high-temperature deformation, plastic mirror body has the same problem. Therefore, the g sensor dash cam lens had better use the glass-metal lens.

How many layers is the lens made up of? There are common 4P( 4 layer resin), G＋2P(2 layer glass＋2 layer resin), 4G(4layer glass), 5G(5layer glass), 6G and so on. What’s the difference between different quantities of glass? That’s imaging quality

We can know that is made of glass through looking the lens, but there are more types of optical glass, and the same glass can also be ground different lenses. It is a great challenge to combine these glasses into a lens with optical properties.

Because add a piece of glass, this indicator is satisfied, but another indicator is over. So it is relatively easy to design a lens with higher imaging quality with more lenses. But the processing has become a problem that it required much of the material and processing technology, so the lens price will double.

In addition, the same is the structure of the lens, different manufacturers of processing capacity are not the same, the price will be very different, the final effect is also different.

Summary: because of the different technology and structure, the price of the lens produced by the different manufacturer has several en yuan difference. So don’t look down on the lens, its quality directly affected the imaging quality. Si manufacturers have been looking for a cheap and good lens, it is a big problem because we can not see the difference from the appearance.